Week 2 - Converging diverging nozzle

Ramjets, scramjets, and rockets all use nozzles to accelerate hot exhaust to produce thrust as described by Newton's third law of motion. The amount of thrust produced by the engine depends on the mass flow rate through the engine, the exit velocity of the flow, and the pressure at the exit of the engine. The value of these three flow variables are all determined by the nozzle design.

A nozzle is a specially shaped tube through which hot gases flow. Ramjets and rockets typically use a fixed convergent section followed by a fixed divergent section for the design of the nozzle. This nozzle configuration is called a convergent-divergent, or CD, nozzle. In a CD nozzle, the hot exhaust leaves the combustion chamber and converges down to the minimum area, or throat, of the nozzle. The throat size is chosen to choke the flow and set the mass flow rate through the system. The flow in the throat is sonic which means the Mach number is equal to one in the throat. Downstream of the throat, the geometry diverges and the flow is isentropically expanded to a supersonic Mach number that depends on the area ratio of the exit to the throat. The expansion of a supersonic flow causes the static pressure and temperature to decrease from the throat to the exit, so the amount of the expansion also determines the exit pressure and temperature. The exit temperature determines the exit speed of sound, which determines the exit velocity. The exit velocity, pressure, and mass flow through the nozzle determines the amount of thrust produced by the nozzle.

Meshing:

• Meshing method selected is face meshing because face meshing provides a mesh which is generated by respecting the curves of the face.
• Face meshing helps to create a neat mesh in this case
• Element size to 4mm
• Name the boundaries as pressure inlet, pressure outlet,axis and wall.

Density-based solver: Flow is compressible and obviously there will be variation in the density.

Axisymmetric

Energy: ON Temperature is involved, so energy equation is required.

Viscous Model: Inviscid Flow is considered as the Inviscid flow to obtain the max efficiency of the nozzle.

Fluid air is set to ideal gas

Pressure inlet: 101325pa

Operating conditions: reference pressure is set to zero

The operating pressure is changed to zero because the flow is a high Mach number compressible flow where the pressure changes are larger than in the low Mach number flows so there is no need to worry about roundoff errors which are more significant in the low Mach number flows. Fluent solver subtracts the operating pressure from absolute pressure to eliminate the roundoff errors, so when operating pressure is set to zero that makes gauge pressure and absolute pressure equal.

Absolute Pr = Atm Pr + Gauge Pr

Pressure outlet: 2533.125Pa

Solution methods: Implicit,least-square cell-based,second-order flow

Initialization Methods: standard initialization calculated from the pressure inlet

Simulation is run with the 600 iterations.

Chart plot was taken for line along axis and line along wall.

RESULTS AND CONTOURS:

AFTER EXPORTING SOLUTION DATA WE CAN PLOT THE VARIATION OF mACH NO. ALONG THE LENGTH OF THE AXIS.